In magnetic type security systems for protecting articles from theft, magnetic targets are employed having detection strips of highly permeable easily saturable magnetic material such as permalloy and deactivation strips of high coercivity, magnetically hard material, such as vicalloy. The deactivation strips are magnetized by a deactivator at a point of sale terminal by subjecting them to a complex magnetic field to neutralize the detection strip. U.S. Pat. No. 4,684,930 shows a deactivator comprising a non-magnetic roller having a magnetic layer comprising a plurality of permanent magnets forming a diamond shaped pattern of magnetization at the surface of the roller.
The diamond shaped pattern is produced by two groups of elongated magnets magnetized transversed to their length and arranged along side each other to form parallel lines of alternate polarity. The magnets of each group form a layer, and the layers formed of the two groups are arranged one on top of the other, with the magnets in one group extending in a different direction than the magnets in the other group. To enable the magnetic field strength from the bottom layer of magnets to be nearly equal to the strength from the top layer at the surface of the roller, the bottom layer of magnets is magnetized more strongly than the top layer.
This method of producing the deactivator suffers from the problems that the manufacturin process is complex and therefore costly, and the resulting field strength in the deactivator is lower than the maximum field strength achievable in the magnetic material.